This invention relates to apparatus for the in-line forming of integral thermoplastic fasteners with thermoplastic film or sheet stock to made into bags, other containers, or other items which are closable or joinable by the fasteners. One way of forming such film or sheet with integral fasteners is that shown in U.S. Pat. No. 4,295,919, assigned to the same assignee as is the present invention. In the embodiments shown in that patent, the film or sheet is extruded through an elongated slot die. The fasteners are separately extruded through a profile die block attached to the side of the die and laterally adjustable along the side of the die so that the fastener profiles can be extruded onto the hot film as it leaves the slot die, the profiles and film body thereby being joined. In such an arrangement, there is no transverse adjustability between the profile die block and the film die and, therefore, the base of the profile which joins the profile to the film is fixed in size and shape unless extrusion is stopped and hardware changes made. Thus, any transverse adjustment in the apparatus of the prior art to change the profile base requires a shutdown of the apparatus. Since the size and shape of the profile base can dramatically affect the operability of the fastener elements, the lack of being able to affect their change during forming has been a shortcoming in the prior art process as respects both operating efficiencies and fastener quality. There, thus, has been a need to have a profile die block which is adjustable in the transverse direction so that the base of the profile is readily adjustable on-line. The present invention makes such on-line transverse adjustability possible.